A channel selecting circuit used in a TV receiver and a CATV converter has a memory apparatus. In the memory apparatus, channel attendant data of each channel including channel skip data, fine tuning data, caption data for displaying a tuned channel number or a name of tuned broadcasting station, etc. are stored.
FIG. 4 illustrates a conventional channel selecting circuit for displaying caption data. The caption data is stored in memory 925. A tuning command having channel data and mode information is supplied to channel selecting circuit 921 from input means 928. The channel data, for instance, specifies a tuned channel with a channel number, and the mode information shows which mode the specified channel belongs to, TV mode or CATV mode. Judging circuit 924 in microcomputer 922 determines whether the specified channel belongs to TV mode or CATV mode based on the mode information. Operating circuit 923 accesses a TV domain 926 of the memory and reads caption data stored therein when the specified channel belongs to TV mode. Operating circuit 923 accesses CATV domain 927 of the memory and reads caption data therein when the specified channel belongs to CATV mode. The accessed caption data is fed to caption processing circuit 914. Regardless of the caption data being stored in the memory or not, operating circuit 923 accesses memory 925 every time the tuning command is fed. The accessed caption data is converted into a caption video signal in caption processing circuit 914, and is fed to a cathode ray tube (hereinafter called CRT) 907 across video signal amplifier 905. Operating circuit 923 also generates a local oscillation controlling signal based on fed channel data, and supplies the signal to tuner 902. Tuner 902 mixes a local oscillating signal of the frequency specified by the local oscillation controlling signal with a TV radio frequency (hereinafter called RF) signal fed from antenna 901. Intermediate frequency (hereinafter called IF) amplifier 903 converts a TV RF signal into an IF signal and also functions as a detector. After detection, the signal is separated into a sound signal and a video signal. The sound signal is supplied to speaker 906 across sound signal amplifier 904. The video signal is supplied to CRT 907 across video signal amplifier 905. The video signal is displayed on CRT 907 by superimposing a caption thereon.
Operating circuit 923, as above described, accesses the memory every time a tuning command is fed, regardless of whether or not the caption data is being stored in the memory. This access, when the caption data is not stored in the memory, is useless and wastes time which deteriorates the response quality of a tuning processing circuit. In order to avoid wasting time, it has been proposed that the channel data and caption data be stored in a random access memory (hereinafter called RAM) of microcomputer 922. However, in most cases, the capacity of RAM is insufficient for this purpose, which proves that this proposal is impractical. According to the present invention, as explained in detail later, the memory device is not accessed when the channel attendant data, including caption data, does not exist. Also according to the present invention, the channel attendant data is not stored in a RAM of a microcomputer while channel data is stored therein. An insufficient RAM capacity thus does not occur.